Solder cone around protruding THT leads (tent structure)

The clipped lead of a soldered THT contact protrudes
THT_LEAD_PROTRUSION_MM (1.5 mm default, 0 disables) out of the hole on
the side opposite the component, and a solder cone wraps it: full
protrusion height at the drill wall, tapering linearly to zero at the
pad edge. Painted as per-cell extra conduction-equivalent copper via
stack.thick_scale - the tall solder column at the wall pulls the joint
vicinity to lead potential (equivalent to extending the barrel wall
vertically), the taper carries the radial spreading. DC-exact additive
conductance; at f > 0 the factor multiplies the skin-corrected sheet
conductance like the via mouths (documented approximation).

The protrusion side is looked up from the owning footprint (pads store
absolute positions; component on F.Cu -> lead tents on B.Cu), with a
logged B.Cu fallback. Dump schema gains protrusion_side and
tht_protrusion_nm (defaults keep older v6 dumps loading).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -125,9 +125,17 @@ SWIG API. Requires KiCad **10.0.1+**.
   soldered **THT joint** additionally assumes the **hole is filled with
   solder** (core in parallel with the plating) and the **pad face
   carries an average-thickness solder coat** (`SOLDER_THICKNESS_UM`,
-  50 µm) over the modeled copper under the pad shape. To model a probe
-  pressed onto the pad face instead, draw a marker rectangle over the
-  pad.
+  50 µm) over the modeled copper under the pad shape. The **clipped
+  lead protrudes** `THT_LEAD_PROTRUSION_MM` (1.5 mm, 0 = off) on the
+  side opposite the component (taken from the owning footprint;
+  assumed `B.Cu` if it cannot be found) and a **solder cone** wraps
+  it: full protrusion height at the drill wall, tapering linearly to
+  zero at the pad edge, applied as extra conduction-equivalent copper
+  per cell. The tall solder column at the wall pulls the joint
+  vicinity to lead potential — equivalent to extending the barrel wall
+  vertically — while the taper carries the radial spreading. To model
+  a probe pressed onto the pad face instead, draw a marker rectangle
+  over the pad.
 - **Contact models** (dialog / `CONTACT_MODEL`): default **uniform
   injection** — a conductor pressed on top feeds the current orthogonally
   with uniform surface density, so |J| ramps across the contact area